The name hamster is derived from the German word Hamster, itself from earlier OHGhamustro, from ORusschoměstorǔ, which is either a blend of the root of Russkhomiak "hamster" and a Baltic word (cf. Lithstaras "hamster")[1] or of Iranian origin (cf. Avhamaēstar "oppressor")[2].

Behavior can vary depending on their environment, genetics, and interaction with people. Because they are easy to breed in captivity, hamsters are often used as lab animals in more economically developed countries. Hamsters have also become established as popular small pets.

Hamsters are crepuscular. In the wild, they burrow underground in the daylight to avoid being caught by predators. Contrary to popular belief they are a nocturnal animal. Their diet contains a variety of foods, including dried food, berries, nuts, fresh fruits and vegetables. In the wild they will eat any wheat, nuts and small bits of fruit and vegetables that they might find lying around on the ground, and will occasionally eat small insects such as small crickets or mealworms. They have elongated fur-lined pouches on both sides of their heads which extend to their shoulders, which they stuff full of food to be brought back to the colony or to be eaten later.

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Hamsters are stout-bodied, with tails much shorter than body length and have small furry ears, short stocky legs, and wide feet. Their thick, silky fur, which can be long or short, can be black, grey, white, brown, buff, yellow, "sapphire" or red depending on the species, or a mix of any of those colors.

Two of the dwarf hamsters belonging to the genus Phodopus (Phodopus campbelli, Campbell's Dwarf Hamster, and Phodopus sungorus, the Winter White Russian Dwarf Hamster) and also two of the species of the genus Cricetulus, (Cricetulus barabensis, the Chinese Striped Hamster, and Cricetulus griseus, the Chinese Dwarf Hamster) have a dark stripe down the middle of the back. The species of genus Phodopus are the smallest, with bodies 5 to 10 cm (about 2 to 4 inches) long; the largest is the common hamster (Cricetus cricetus), measuring up to 34 cm (about 13 inches) long, not including a short tail of up to 4 cm (1-1/2 inches). The Angora hamster, also known as the long-haired or Teddy Bear hamster, which is a type of the Syrian Hamster is the second largest hamster breed, measuring up to 15 cm (about 6 inches) long.

The tail is often difficult to see; usually it is not very long, and on a long haired hamster it is barely visible. Hamsters are very flexible, and their bones are somewhat fragile.

Hamsters' northern range extends from central Europe through Siberia, Mongolia, and northern China to Korea. The southern portion of their range stretches from Syria to India. Throughout dry, open country they inhabit desert borders, vegetated sand dunes, shrubby and rocky foothills and plateaux, river valleys, and mountain steppes; some live among cultivated crops. Geographic distribution varies greatly between species. The common hamster, for example, is found from central Europe to western Siberia and northwestern China, but the golden hamster has been found only near a small town in northwestern Syria.[3]

Hamsters are omnivorous. Their diet consists mostly of grains (such as whole grain oats and corn) but also includes fresh fruit, roots such as carrots, green parts of plants. Hamsters carry food in their spacious cheek pouches to a cache in the burrow. When full, their cheeks can make their heads double in size. Hamsters in the Middle East have been known to hunt in packs to find insects for food.[3]

Syrian hamsters (Mesocricetus auratus) are generally solitary and will fight to the death if put together, whereas some of dwarf hamster species can get along with others of the same species. Hamsters are primarily considered crepuscular and at one point were considered nocturnal as they are sometimes active all night. Some species have been observed to be more nocturnal than others. All hamsters are excellent diggers, constructing burrows with one or more entrances and with galleries that are connected to chambers for nesting, food storage, and other activities. They will also appropriate tunnels made by other mammals; the Winter White Russian Dwarf Hamster (Phodopus sungorus), for instance, uses paths and burrows of the pika. None hibernate during winter, but some (mostly Syrian hamsters) experience periods of torpor lasting from a few days to several weeks. This probably means that conditions are too cold for them. Hamsters are known to stockpile large amounts of food, because of natural instinct from the wild. Because of this behavior it is possible to leave a hamster alone for a few days.
Once a Syrian hamster is tamed, they remain so for a long time. However, dwarf hamsters must be continuously played with otherwise if left alone for a maximum of two to three weeks, it can become untame again.[3]

Hamsters become fertile at different ages dependent on their species, but this can be from one month to three months of age. Male hamsters remain fertile for the rest of their lives, though females do not. Females are in heat approximately every four days.

Breeding season is from April to October, with two to five litters of 1 to 13 young being born after a gestation period of 16 to 23 days.[3] Gestation lasts 16 to 18 days for Syrian hamsters, 18 to 21 days for the Russian hamsters, 21 to 23 days for Chinese hamsters and 23 to 30 for Roborovski Hamsters. The average litter for Syrians is about 7, but can be as great as 24, which is the maximum number of pups that can be contained in the uterus. Campbell's Dwarf Hamsters tend to have 4 to 8 in a litter but can have up to 14. Winter White Russian Dwarf Hamsters tend to have slightly smaller litters, as do Chinese and Roborovski hamsters.

Siberian hamsters form close, monogamous bonds with their mates. If separated, they may become very depressed. This happens especially in males. Males will become inactive, eat more, and even show some behavioral changes similar to some types of depression in humans. This can even cause obesity in the hamster.

Chinese hamster females are known for being aggressive toward the male if kept together for too long. In some cases, male Chinese hamsters have died after being attacked by the female. If breeding Chinese hamsters, it is recommended to separate the pair after mating or the hamsters will attack each other.

Hamsters are born hairless and blind in a nest which the mother will have prepared in advance. She uses shredded material such as leaves in the wild but prefers cotton or toilet paper in captivity. After one week they begin to explore outside the nest. They are completely weaned after three weeks, or four for Roborovski Hamsters. Most breeders will sell the hamsters to shops when the hamsters are anywhere from two to eight weeks old.

Taxonomists generally disagree about the most appropriate placement of the subfamily Cricetinae within the superfamily Muroidea. Some place it in a family Cricetidae that also includes voles, lemmings, and New World rats and mice; others group all these into a large family called Muridae. Their evolutionary history is recorded by 15 extinct fossil genera and extends back 11.2 million to 16.4 million years to the Middle Miocene Epoch in Europe and North Africa; in Asia it extends 6 million to 11 million years. Four of the seven living genera include extinct species. One extinct hamster of Cricetus, for example, lived in North Africa during the Middle Miocene, but the only extant member of that genus is the common hamster of Eurasia.

The best-known species of hamster is the Syrian or Golden Hamster (Mesocricetus auratus), which is the type of hamster most commonly kept as a pet. It is also sometimes called a "fancy" hamster. Pet stores also have taken to calling them "honey bears," "panda bears," "black bears," "European black bears," "polar bears," "teddy bears," and "Dalmatian", depending on their coloration. There are also several variations, including long-haired varieties that grow hair several centimeters long and often require special care.

Other hamsters that are kept as pets are the four species of "dwarf hamster". Campbell's Dwarf Hamster (Phodopus campbelli) is the most common of the four — they are also sometimes called "Russian Dwarfs"; however, many hamsters are from Russia, and so this ambiguous name does not distinguish them from other species appropriately. The coat of the Winter White Russian Dwarf Hamster (Phodopus sungorus) might turn white during winter (when the hours of daylight decrease). The Roborovski Hamster (Phodopus roborovskii) is extremely small and fast. The Chinese Hamster (Cricetulus griseus), although not technically a true "dwarf hamster", is the only hamster with a prehensile tail (about 4cm long) - most hamsters have very short, non-prehensile tails.

Many breeders also show their hamsters and so breed towards producing a good healthy show hamster with a view to keeping one or two themselves so quality and temperament are of vital importance when planning the breeding. Although breeders of show hamsters specialise in breeding show hamsters, there are also owners who have bred their pet hamsters. These may be the result of a planned or unplanned pregnancy but the hamsters have usually been cared for well and handled regularly, so make very suitable pets. Buying a hamster directly from a breeder means that there is the opportunity to see the parents and know the dates of birth.

In Australia it is illegal to keep hamsters as pets as 'escapees' could breed in the wild and become 'feral' pest animals.

Syrian hamsters typically live no more than two to three years in captivity, less than that in the wild. Russian Hamsters (Campbell's and Winter White) live approximately 1.5 to 2 years in captivity, and Chinese Hamsters 2.5 to 3 years. The smaller Roborovski Hamster often lives to 3 to 3.5 years in captivity. Both Syrian and Russian hamsters mature quickly and can begin reproducing at a young age (4–5 weeks), whereas Chinese hamsters will usually begin reproducing at 2–3 months of age, and Roborovskis at 3–4 months of age.

Left to their own devices, hamsters will produce several litters a year with several pups in each litter. When seen from above, a sexually mature female hamster has a trim tail line; a male's tail line bulges on both sides. This might not be very visible in all species. Male hamsters typically have very large testes in relation to their body size. Before sexual maturity occurs at about 4–6 weeks, it is more difficult to determine a young hamster's sex. When examined, female hamsters have two holes close together, whereas males have anal and genital openings further apart than the female's. (The penis is usually withdrawn into the coat and thus appears as a hole or pink pimple.)

The genus Phodopus was found to represent the earliest split among hamsters. Their analysis included both species. The results of another study (Lebedev et al., 2003) may suggest that Cricetulus kamensis (and presumably the related C. alticola) might belong to either this Phodopus group or hold a similar basal position.

Mesocricetus group

The genus Mesocricetus also form a clade. Their analysis included all four species, with M. auratus and M. raddei forming one subclade and M. brandti and M. newtoni another.

Remaining genera

The remaining genera of hamsters formed a third major clade. Two of the three sampled species within Cricetulus represent the earliest split. This clade contains Cricetulus barabensis (and presumably the related C. sokolovi) and Cricetulus longicaudatus.

Miscellaneous

The remaining clade contains members of Allocricetulus, Tscherskia, Cricetus, and Cricetulus migratorius. Allocricetulus and Cricetus were sister taxa. Cricetulus migratorius was their next closest relative, and Tscherskia was basal.

Note that there are some rodents which are sometimes called "hamsters" that are not currently classified in the hamster subfamily Cricetinae. These include the Maned Hamster or Crested Hamster, which is really the Maned Rat (Lophiomys imhausi), although not nearly as marketable under that name. Others are the mouse-like hamsters (Calomyscus spp.), and the white-tailed rat (Mystromys albicaudatus).